The invention concerns a method of improving the soil-release properties of a fabric consisting of synthetic fibres and/or thread materials. The invention is applicable to a large number of various types of weaves of different materials and types of threads but it is primarily designed to improve polyester monofilaments used in the manufacture of forming fabrics for papermaking and cellulose machines and for filter cloths used in the papermaking and cellulose industries and related industries. The improvement consists of the addition to the fibrous and/or thread material of polymers of a kind that make it possible to improve considerably the hydrophilic properties of the fabric compared with those hitherto obtainable in prior-art fabrics.
The invention will be described with reference to its applications in forming fabrics for the purpose of improving the soil-repellant properties of such fabrics. The impurities present in the paper pulp which is dewatered in the wet section of the papermachine have a tendency to clog the wire, the latter therefore having to be cleaned from time to time. Usually, the cleaning is effected by spraying the wire by means of powerful water jets (high-pressure jet sprays), which has a strong wearing effect on the fabric. It has therefore been customary to subject the fabrics to a treatment making them soil-repellant. The impurities most commonly found in paper pulps are oily or tarry soils. Consequently, the fabric will be soil-repellant, if its hydrophilic properties are increased, that is, if its wetting properties are improved. Hitherto, this has been achieved by treating the fabric with caustic soda, since the fabrics commonly used today often consist of polyester monofilaments, and by treating such fabrics with caustic soda the polyester is hydrolized, increasing the wetting properties of the filaments. However, treatments of this kind have an effect only on the surface layer of the filaments, and this surface layer is soon worn off or rendered ineffective.
Attempts have also been made to use direct hydrophilic surface treatments of the fibrous and/or thread material, primarily by coating the surface with a hydrophilic type of latex. However, treatments of this kind require large quantities of chemicals and careful supervision. Just as is the case in caustic soda treatments this surface-coating treatment affects only the surface layer of the filament and the coating is worn off after a short period of use.
For certain types of fabrics admixture of initially hydrophilic substances prior to extrusion has been discussed. Since extrusion must be carried out in an environment that is absolute void of moisture there are considerable problems of a process-technical nature that must be solved to effect admixture of moisture-absorbing substances. These problems are most prominent in the extrusion of monofilament threads of the kind used in forming fabrics and filter cloths.